Abstract: Background and purpose: Vitamin D (VitD) is a steroid hormone. This study aimed to detect the level of 25-hydroxy VitD ［25 (OH) D］ which is a serum biomarker of VitD status in peripheral blood of patients with breast cancer, and to explore the correlation between VitD and clinicopathologic characteristics of breast cancer patients. Methods: We measured the level of 25 (OH) D in 109 breast cancer patients, 50 patients with benign breast tumors and 2 000 healthy subjects in our hospital from January 2015 to July 2018 by a chemiluminescent immunoassay method. Flow cytometry was used to detect the immune function of T cells and the level of NK cells in the peripheral blood of breast cancer patients. Furthermore，the expression of VitD receptor (VDR) in breast cancer tissues was detected by immunohistochemistry. Results: The level of 25 (OH) D in peripheral blood of patients with breast cancer was significantly lower compared with patients with benign breast tumors or healthy subjects (P<0.05). There was no significant difference in peripheral blood 25 (OH) D levels between patients with benign breast tumors and healthy subjects (P>0.05). The level of 25 (OH) D in breast cancer patients was significantly associated with the immune function of T cells (CD4⁺/CD8⁺ ratio), clinical stage, lymph node metastasis, bone metastasis and progesterone receptor (PR) positivity, whereas serum 25 (OH) D level had no relation to the tumor size, the quantity of NK cells and the level of estrogen receptor (ER) (P>0.05). There was a statistically significant correlation between the expression of VDR in breast cancer tissues and the level of hormone receptor (ER and PR) (P<0.05), while positive expression of VDR was not associated with the immune function of T cells, clinical stage, tumor size, bone metastasis and lymph node metastasis (P>0.05). Conclusion: Low levels of VitD in peripheral blood may be associated with high risk of breast cancer, poor T cell immune function and poor prognosis.

Key words: 25-hydroxy vitamin D, Vitamin D receptor, Breast cancer